Question

The formula of the chromium $\left( {III} \right)$ ion is $C{r^{ + 3}}$ and of the sulphate ion is $S{O_4}^{2 - }$ . Give the formula of chromium $\left( {III} \right)$ sulphate.

Answer 1

Hint: We can use criss-cross method to find the formula of chromium(III) sulphate. In this method, the charge of the ion is crossed over to become the subscript of the other ion i.e., the charges are interchanged between each other.

Complete step by step solution:
Chromium is an element with the symbol Cr and its atomic number is 24. It is the first element in group 6. The electronic configuration of chromium is 2, 8,13,1. The +3 and +6 states occur the most commonly within chromium compounds. Chromium (III) ion can be obtained by dissolving elemental chromium in acids like hydrochloric or sulphuric acid and it can also be formed through the reduction of chromium (VI) by cytochrome (redox-active proteins) c7.
Sulphate ion is a polyatomic anion with the formula of $S{O_4}^{2 - }$ . Sulphates are salts of sulphuric acid and are prepared from that acid. The sulphate ion consists of a central sulphur atom which is surrounded by four equivalent oxygen atoms in a tetrahedral arrangement. It carries a charge of $ - 2$ .
The chromium ion is represented by the symbol $C{r^{3 + }}$ and sulphate ion is represented by $S{O_4}^{2 - }$ . The positive sign on the chromium ions means it is a cation with a charge $ + 3$ and the negative sign on sulphate ion means it is an anion with a charge of $ - 2$ . From the criss-cross method i.e., interchange of charges between the ions, we can find the formula of chromium sulphate. The charge on chromium ion is written as a subscript after the sulphate ion and similarly the charge on sulphate ion is written as a subscript after the chromium ion. Hence, we get the formula of chromium (III) sulphate as $C{r_2}{\left( {S{O_4}} \right)_3}$ . Now, we’ll show by the diagram i.e., by a criss-cross method,

Therefore, the formula of chromium(III) sulphate is $C{r_2}{\left( {S{O_4}} \right)_3}$ .

Note: We should remember that the charge on Chromium ion is exchanged with the sulphate ion i.e., $ + 3$ charge on chromium ion is written as the subscript of sulphate and similarly $ + 2$ charge on sulphate ion is written as the subscript of chromium (III) ion.